1. Field of the Invention
The present invention relates to a method and an apparatus for continuously measuring a concentration of an oxidant or a reductant in a process fluid in a chemical plant, etc. by utilizing dependency of currents for concentrations in an electrolytic oxidation or reduction of the oxidant or reductant on a working solid electrode made of gold, platinum, carbon-paste etc.
2. Description of Prior Arts
A concentration of an oxidant or a reductant has been measured by various methods. A potentiostat has been used for the measurement of a concentration of an oxidant and a reductant. However, the continuous measurement of the concentration of an oxidant or a reductant has not been satisfactorily achieved.
An electrochemical measurement for analyzing current-potential characteristics by applying a voltage to a working solid electrode set in a fluid has been known as a hydrodynamic voltammetry. The current-potential characteristic curves obtained by the hydrodynamic voltammetry are similar to those of polarography used in various fields. However, waves obtained in a laminar flow control have not the current oscillation caused by using a dropping mercury electrode, and height of the limiting diffusion current in the current-potential characteristic curve is usually high. A height of a limiting diffusion current is proportional to a concentration of an oxidant or a reductant in a solution and is used for a quantative analysis.
When the wave is a reduction wave in a simple oxidation-reduction system ##STR1## wherein Ox: oxidant; e: electron; and Red: reductant, the relation of EQU Id.alpha.Cox
wherein Id: limiting diffusion current; and Cox: concentration of oxidant, is given in both of the polarography and the hydrodynamic voltammetry. The limiting diffusion current Id can be also shown by the equation: EQU Id=K.F.Cox
wherein K: constant; and F: function given by flowing condition.
The hydrodynamic voltammetry is mainly classified into two methods.
In one method, an electrode is moved in a solution in the stationary condition. The typical one is to use a rotating disk electrode.
In the other method, a solution is forcibly flowed toward an electrode in the stationary condition. The former has been mainly studied. However, the former method has disadvantages that a mechanical sliding part is needed as an electric contact for the rotating disk electrode, and a synchronous motor having no fluctuation of rotary speed is needed in the continuous measurement of a concentration of an oxidant or a reductant in an industrial process fluid, and the maintenance is not easy in view of anticorrosive and durable property.